Microcircuits typically include a number of semiconductor devices which generate heat during operation. As microcircuit geometries become increasingly smaller, the heat density increases. Heat output of devices is also increased as devices operate at higher clock frequencies. Operation of semiconductor devices can be degraded at high temperatures, and thus it is desirable to remove this heat from the microcircuit. With the trend to smaller and faster devices, heat removal has become more difficult.
Heat removal is typically provided by attaching the microcircuit to a heat sink. For example, the electronic devices in the microcircuit are typically constructed on one side of a substrate and the back side of the substrate is attached to a heat sink. While heat removal using such an approach is possible, the heat must flow through the substrate, limiting the effectiveness of cooling.
Increasingly complex microcircuit structures are being used which further complicates heat removal. One example is microcircuits which include fabrication on both sides of a silicon waver. Another example is three-dimensional circuits which are implemented by chip stacking or multi-chip modules. As yet another example, optical interconnect layers may be placed on top of active circuitry layers to augment or replace conventional metal interconnect. With these complex structures, electronic devices can generate heat deep within a structure which it is difficult to remove.